Integrated photoluminescence intensity,
A new characterization method based on hyperspectral imaging recording spectrally resolved images allows the cartography of electroluminescence (EL) and photoluminescence (PL). From the data acquired, spatial variations of cell properties such as open circuit voltage and transport mechanisms were identified and characterized. Furthermore, the system was compared to a classical confocal microscope, showing significant gains in acquisition time.
Spectrally resolved images provide considerable advantages such as, absolute calibration of intensity, micrometer scale resolution, and excitation and detection on a surface (no information loss from lateral diffusion and roughness). In luminescence imaging, absolute calibration is a main concern and is here done in two steps: first, an absolute calibration at a determined point (spatially and spectrally) with a laser, and then a relative calibration on the whole space and the whole spectrum, with a calibrated lamp coupled to an integrating sphere.The images rendered by IMA are spectrally resolved luminescence images from multicrystalline CIS solar cell, offering means of studying its spatial inhomogeneities. On high efficiency GaAs solar cells, we got absolute measurements of EL and successfully investigated reciprocity relations. Our next step is to record quantitative maps of CIGS physical properties from PL and EL images, such as VOC , transport parameters and more.
A confocal microscope coupled to a spectrometer provides similar data. The 532nm laser is focused onto the cell front contact, and the cartography of PL spectra is obtained by scanning the sample. The acquisition time with the imager is much faster. 150*150µm² at 107 W/m² would take hundreds of hours in confocal, but only 8min with IMA. Moreover, surface excitation and detection allow to get rid of diffusion and roughness troubles for quantitative analysis.
A. Delamarre¹*, L. Lombez¹, J.F. Guillemoles¹, M. Verhaegen², B. Bourgoin²